Hitherto, in a legged mobile robot, e.g., a bipedal mobile robot, the robot is mainly adapted to perform walking. In recent years, however, as the development of legged mobile robots advances, it has come to be desired that the robot also run at a faster speed or jump rather than performing only walking.
When a robot is walking, it supports its own weight by having one of its legs in contact with the ground. If the robot is to run or jump, there will be a period in which a floor reaction force acting on the robot becomes zero or nearly zero. Accordingly, for the robot to run or jump, it will be important to control also the floor reaction force acting on the robot, especially a vertical component of a translational force.
Accordingly, the present applicant has proposed, in previously submitted PCT application No. PCT/JP02/13596, etc., a control device for achieving running or the like by generating a desired motion pattern based on a dynamic model of a robot while explicitly designing a desired ZMP pattern and a desired floor reaction force vertical component (the vertical component of a translational force, which will apply hereinafter) pattern and by carrying out control so as to cause a vertical component of an actual floor reaction force to follow a desired floor reaction force vertical component pattern by compliance control while making an actual robot follow the desired motion pattern.
In the above PCT application No. PCT/JP02/13596, compliance control for controlling floor reaction force vertical components proposed in Japanese Patent Laid Open Application No. 11-300661 is used. In the compliance control, a distal end (foot) of a leg is displaced in the vertical direction with respect to a body of a robot(shifted from the position of the distal end of the leg of a desired gait) on the basis of an actual floor reaction force vertical component. This will be hereinafter referred to as vertical compliance control.
There has been a tendency in which, if the vertical compliance control is not used, then a kicking force at a jump is significantly influenced by the hardness of a floor. For instance, there have been cases where an appropriate jumping force is obtained on a hard floor, whereas an insufficient jumping force results on a carpet. There have also been cases where it is difficult for generated characteristic vibrations to attenuate, depending on flexture rigidity of a floor, the rigidity of a robot, and the mass of a robot. Especially in the case of a floor made of an iron plate or the like with low attenuation property, characteristic vibrations do not attenuate for a long time, and contact with the ground is impaired, causing slippage.
However, if the vertical compliance control is used to eliminate the inconvenience, then the actual vertical position of the robot body (hereinafter referred to as the actual vertical position of the body) will be easily shifted from a desired vertical position of the body, frequently causing a shifted timing of leaving a floor at a jump. For instance, if the actual vertical position of the body is lower than a desired vertical position of the body at desired floor leaving time, then the vertical component of a floor reaction force does not reach zero when the desired floor leaving time is reached, resulting in a delayed floor leaving timing.
Conversely, if the actual vertical position of the body is higher than a desired vertical position of the body at a desired floor leaving time, then the vertical component of a floor reaction force reaches zero before the desired floor leaving time, resulting in an advanced floor leaving timing. Complementarily, if the vertical compliance control is not used, then the actual vertical position of the body substantially coincides with a desired vertical position of the body, making it difficult for a floor leaving timing to be disturbed.
If the floor leaving timing is advanced as described above, then a frictional force in a horizontal direction decreases or becomes zero earlier than estimated, so that slippage or spin has frequently taken place.
Conversely, if the floor leaving timing is delayed, then there has been a danger of a free foot being caught on a floor before the free foot is moved forward immediately after leaving the floor when running.
Furthermore, if a trajectory of the vertical position of the body of an actual robot (the trajectory of center of gravity) deviates from a desired trajectory of the vertical position of the body when leaving a floor, then the trajectory of the center of gravity deviates also when landing, causing the landing timing to be disturbed. Hence, there has been a danger in that an excessive ground speed results when a free leg foot lands, generating a large landing impact.
Furthermore, deviation of the motion and a floor reaction force of the actual robot from those of a desired gait has led to deteriorated posture stability.
The present invention has been made in view of the aforesaid background, and it is an object thereof to provide a control device of a legged mobile robot that makes it possible to bring a trajectory of a leg distal portion (foot) of a robot relative to a floor close to the trajectory of a leg distal portion (foot) of a desired gait, to ensure the robot to leave a floor at a floor leaving timing according to the desired gait so as to prevent the robot from slipping or spinning or a free leg from being caught on a floor, and to reduce landing impacts.